Problem: A box contains $5$ red balls, $7$ green balls, and $11$ blue balls. If a ball is randomly chosen, what is the probability that it is not red?
Explanation: There are $5 + 7 + 11 = 23$ balls in the box. There are $5$ red balls. That means $23 - 5 = 18$ are not red. The probability is $ \frac{18}{23}$.